Accurate geographic tracking of mobile devices

ABSTRACT

A tracking system is described having at least two mobile transmitter/receivers (“transceivers”) which sense and respond to at least one tracking transceiver. The signals sent to and received from the mobile transceivers are analyzed to get a distance (range) that each is from the tracking transceiver. This can be converted into a position relative to the mobile transceivers. If there are enough transceivers, and at least one knows its absolute location, the absolute location of the mobile transceivers may be determined. Existing smartphones, cellphones, WI-FI® wireless standard routers, BLUETOOTH® wireless standard devices, and near-field devices that have on-board processors, can be modified to run executable code to implement the current invention. They may communicate using at least one of the modalities for tracking. These may be implemented in tracking the position and orientation of moving devices, such as a head-mounted display for virtual/Augmented Reality, automobiles, packages in a package delivery truck. The system may also be implemented to identify and keep track of the last known location of various objects.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. provisional application No. 62/115,954, filed Feb. 13, 2015, entitled “Utilizing Radio Frequency Signals Transmitted by Stationary or Mobile Devices for Accurate and Geographically Broad Tracking of Mobile Devices in the Real World, Augmented Reality or Virtual Reality”, the entirety of which is incorporated by reference herein.

BACKGROUND

Field of Invention

The present invention relates to a system for tracking of the position of multiple objects utilizing radio frequency (RF) transmitters, and more specifically to a highly accurate system for tracking the position of multiple objects that may be implemented indoors.

Description of Related Art

Determining the position of an electronic device or object has been a subject of much research since the emergence of RADAR and SONAR. A variety of proximity and position detection schemes exists today. For example, the Global Positioning System (GPS) has been transformational to military and civilian users by providing a system of orbiting satellites that have highly synchronized clocks emitting timing information continuously. A GPS receiver obtaining signals from three satellites can triangulate its position with time of receipt information. This triangulation is accurate to meters and is highly suitable for use in navigation for oceanic ships, cars or when walking. However, GPS signals do not provide accuracy to five inches or less as would be desirable in a Virtual Reality (VR) and Augmented Reality (AR) systems. VR technologies simulate an environment and typically provide a view of this environment on a head mounted display (HMD) which may also provide headphones with synthesized sound. AR technologies provide images which are partially of actual object with synthesized computer generated images superimposed upon it. VR and AR technologies are described in U.S. patent application Ser. No. 13/967,058 filed Aug. 14, 2013, issued as U.S. Pat. No. 9,519,344 on Dec. 13, 2016, and Ser. No. 14/614,734 filed Feb. 5, 2015, issued as U.S. Pat. No. 10,200,819 on Feb. 15, 2019, owned by the owner of this application, and are hereby incorporated by reference as if set forth in their entirety herein.

GPS systems do not work as well indoors. Many indoor tracking systems have been proposed. Apple iBeacons, for example, use Bluetooth Low Energy (BLE) transceivers to transmit beacon identification (and other) information and the location of a receiver from the iBeacon is calculated based on Received Signal Strength Indicator (RSSI). Such a system is a proximity indicator, and does not provide a high level of location accuracy necessary in many modern applications. There have been other attempts at accurate indoor wireless positioning systems, including for example the IEEE paper “Improving WLAN-Based Indoor Mobile Positioning Using Sparsity”, by Pourhomayoun and Fowler (2012). However, to date, such systems have accuracy of about a meter, which is not adequate for real time tracking of position in many applications.

The above tracking systems have multiple uses in gross position determination. However, more recently, the need has arisen for precise location and tracking of objects or devices, both indoors and outdoors. Wireless tracking is described more fully in U.S. patent application Ser. No. 14/600,025 filed Jan. 20, 2015, published on May 14, 2015 as U.S. Pub. No. US 2015-0130664 A1, and Ser. No. 14/354,833 filed Apr. 28, 2014, issued as U.S. Pat. No. 9,945,940 on Apr. 17, 2018, owned by the owner of the this application and are hereby incorporated by reference as if set forth in their entirety in this application. For example, VR and AR technologies are starting to emerge as viable interactive means of communicating, working, playing, and exploring with the digital world. To make these new AR and VR systems more effective, the need for improved accuracy and faster response in these systems increases. These improved systems must contemplate the user experience from the moment they begin interacting with the ARlVR system, thru its use and return to a disconnected world. Such an immersive experience requires precise real time tracking of the user for a realistic experience.

U.S. Pat. No. 8,749,433 issued Jun. 10, 2014, discusses a system for tracking an RF transmitter. If attached to an object, tracking this RF transmitter will also track the attached object.

This type of tracking has been integrated into a virtual reality system as discussed in U.S. patent application Ser. No. 14/614,734, filed Feb. 5, 2015, issued as U.S. Pat. No. 10,200,819 on Feb. 15, 2019, owned by the owner of this application, and hereby incorporated by reference in its entirety herein. In such a system, a transmitter transmits its location, and multiple receiver antennae and a controller use time difference of arrival (TDOA) to determine the position of the transmitting device. This allows the tracking to be precise; however, if only one transmitter is utilized, then only one transmitter (point) may be tracked.

Another technique for internal tracking of objects is described in the paper “Multifrequency-Based Range Estimation of RFID Tags” (2009, IEEE, by Xin Li). In this paper, multiple frequencies are compared using a phase difference of arrival (PDOA) to locate or track objects. The radiofrequency identification (RFID) tags employed with the present system include a means for transmitting and receiving RF signals, a processor, memory which may include executable code and possibly sensors. The RFID tag can then execute a program and function as described herein.

In this technique, multiple frequencies are transmitted to an RFID, which retransmits the frequencies as is known to those skilled in the art. The returned signal can be used to calculate the distance from the transmitter to the RFID. However, analysis of the returned signal only provides a distance measurement from the transmitter to the RFID tag. Several tags must be used to determine directionality.

Of particular interest in AR and VR are virtual reality glasses and/or head mounted displays (“HMDs”). As HMDs become more prevalent, new functionality to enable better engagement with and connection to the virtual world become critical.

There are a variety of approaches that attempt to provide an intuitive interface for controlling content shown on these devices—as is critical to the effectiveness of how HMDs are used. As most of these HMDs will be wireless and mobile, operated away from desks or related environments where computer mouse or trackpads are accessible, there needs to be an effective solution for providing input control without requiring a typical input device. Cameras can be installed on the HMDs to track a person's hand gestures and these gestures can then be used for interaction. But, in these camera-based systems, gesture tracking can be limited by the field of view of the camera, accuracy of the camera gesture tracking, range detection of the hand position as viewed by HMD cameras, or the lack of tactile input to the hand or fingers as they are interacting with the program running on the HMD.

Most VR/AR systems require recalibration of the tracking system when the number of tracked objects changes. This make the systems difficult to properly configure and impractical for certain uses.

The geographic area in which objects may be tracked is typically limited. The objects must be within the transmission range of the transmitters. Once the objects are outside of this area, they can no longer be tracked.

Some prior art tracking systems require significant RF transmission that require significant energy to operate. If a user would like to continuously track objects, then the amount of power dissipation becomes significant. This power dissipation reduces battery life.

Barcode readers and mobile scanners are described in U.S. patent application Ser. No. 14/568,468 filed Dec. 12, 2014 which is owned by the owner of this application and hereby incorporated by reference as if set forth in its entirety herein.

While the above systems for tracking are useful, they do not provide a suitable method of tracking objects with precision and in real time. Furthermore, they do not address real time tracking of multiple objects in a coordinated way as would be required in an AR or VR environment. Currently there is a need for highly accurate and low power tracking systems for indoor and outdoor tracking of multiple points on multiple objects.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the system described in this application will become more apparent when read with the exemplary embodiment described specification and shown in the drawings. Further, in the accompanying drawings and description that follow, like parts are indicated throughout the drawings and description with the same reference numerals, respectively. The figures may not be drawn to scale and the proportions of certain parts have been exaggerated for convenience of illustration.

FIG. 1 is a schematic illustration of a head-mounted display (HMD) being tracked by a tracking system according to one embodiment of the present invention.

FIG. 2 is a schematic illustration of the major elements of an HMD receiver according to one embodiment of the present invention.

FIG. 3 illustrates how inaccurate tracking leads to image distortion in virtual reality systems.

FIG. 4 is an illustration of the use of mobile devices to create more accurate location determinations.

FIG. 5 illustrates the use of the tracking system implemented in two different automobiles to predict and prevent collisions.

FIG. 6 shows location and orientation determinations for HMD in two dimensions using a single transmitter and two receiving antennae.

FIG. 7 shows location and orientation determinations for the HMD in three dimensions using a single transmitter and three receiving antennae in different planes.

SUMMARY

An accurate and intuitive approach for interfacing with devices having RF capabilities, such as HMDs, mobile devices and the like, without camera gesture tracking, can enable new use cases and more effective control of content shown on these devices. As most HMDs will have radio communication capabilities, a means to leverage this functionality to enable interaction is helpful and economical. A method to enable HMDs to use their basic radio communication to accurately track their own position as well as the position of input devices in free space can enable better interaction as well as reduce costs.

The HMD would have two or more antennae embedded in or mounted to the HMD. A multifrequency transmitter, such as an Access Point, provides two or more frequency signals to the two or more HMD antennae. The HMD uses these two signals as received at each antenna to identify the range between the antenna and the Access Point. Then, using both (for two HMD antennae) ranges from either one or more Access Points with known position coordinates and the heading and orientation as supplied by inertial sensors in the HMD, the HMD can determine accurate position information.

Position can be further defined and accuracies improved using RF signals from additional Access Points, transmitters sending location information, motion sensors (including GPS, magnetic, accelerometer, gyroscope) or other position and/or orientation information sources.

The present disclosure also provides the ability for an HMD to accurately track the relative three-dimensional position of a wireless transmitting device such as an RFID device, or such as a phone, ring, wristband, stylus, handheld pointer, or related interactive peripheral device, (“Tag”), using the same multifrequency transmitting method described above for Access Points communicating range to the HMD. This relative position tracking would provide a flexible and intuitive approach for HMD interaction. Tags could become intuitive, interactive peripherals for HMDs and provide a unique and effective means to engage with programs displayed on the device without requiring a mouse, trackpad, camera, or related input solution.

HMDs can track the position of a Tag and use the position data to engage with a software program running or displayed on the device. In these applications, the Tag position and movement would be registered with screen images provided by software and shown on the HMD. To make this Tag's operation effective for a user (to control a cursor on a screen for example), very high position accuracies are required to provide realistic interaction between the user operating the Tag and the software program shown on the HMD. Herein is described a method that can provide said tracking capability for the HMD to meet the accuracy and cost requirements of these devices but also work with hardware constraints inherent in the size and ergonomic restrictions of HMDs.

In one embodiment of the present disclosure there is a system that allows Mobile Devices such as augmented or virtual reality glasses, robots, drones, handheld communicators (mobile phones) or scanners, or any mobile peripheral (Mobile Device) with radio frequency (RF) communication capability and multiple antennae embedded or attached to the mobile device, to track other devices that emit electromagnetic or RF signals (Other Devices) relative position to the Mobile Device. Further, when multiple Mobile Devices are present, each can calculate and communicate its own position relative to other devices, and the web of devices can provide a means for more efficiently and accurately tracking other devices. In addition, the Mobile Device may determine its actual outdoor or indoor position by utilizing certain stationary devices (Access Points) with RF communication capability and the ability to provide the Mobile Device with the Access Points' two or three-dimensional position coordinates. This position can then be relayed to other Mobile Devices or to a tracking center in certain use cases.

The current invention may be embodied as a system for tracking mobile devices in real time having a multifrequency transmitter, the transmitter is adapted to transmit identification and position information of the transceiver. It includes a mobile device having a user display that provides images to a user as viewed from a specified viewpoint, at least two mobile display antennae mounted on the display adapted to receive signals from the multifrequency transmitter, a receiver circuit having a carrier recovery circuit that functions to synchronize the signals received by each wireless, compare their phases and determine phase differences; and a processor running coupled to the receiver circuit, adapted to run executable code. The executable code functioning to receive the phase differences from the receiver circuit, calculate the distance from a multifrequency transmitter to each antenna based on phase differences, and calculate the position of each antenna based on the calculated distances, and causing the images provided to the user to have viewpoint based upon the calculated positions of each antenna.

The current invention may also be embodied as a system for tracking the location of movable objects having a plurality of transceivers being capable of BLUETOOTH® wireless standards, WI-FI® wireless standards, cellular and near field communication. Each transceiver has a transmitter capable of transmitting an RF signal a receiver capable of receiving an RF signal, a processor capable of running prestored executable code. The executable code, when run causes a requesting transceiver to broadcast a signal requesting nearby transceivers to transmit a signal back which includes an identifier of the transceiver, determine a range from each corresponding transceiver, and calculate, from the plurality of received signals, a location of the requesting transceiver.

The current invention may also be embodied as a method of tracking a position of a movable objects by providing at least two tracked transceiver at known locations relative to the tracked object, employing a least two node transceiver which will return a signal when requested and transmit their identity in the signal, transmitting from the node transceivers, and indication of their presence, requesting from the tracked transceivers, that the node transceivers send a reply, receiving at the tracked transceivers the signals from each of the node transceivers, determining a distance between the each node transceiver and tracked transceiver, and using the known positional locations of the tracked transceivers to the movable object, and calculating the position of each tracked transceiver, and the movable object relative to the node transceivers.

DETAILED DESCRIPTION

Basic Tracking

FIG. 1 shows a tracking system 100 for tracking a mobile object, such as a mobile display or a head mounted display device (HMD) 300 that has a display 309 for each of the user's eyes, and two or more antennae 301, 303, attached to, or embedded in said HMD 300. The antennae 301, 303 are designed to be a known, fixed distance apart, and a known fixed distance from each of the displays 309. The HMD 300 may employ side arms 305, 307, like those of eyeglasses to hold the HMD 300 to the user's head in the proper position. Alternatively, the HMD may be held in place with straps or other commonly known suitable attachments.

Access points 210, 220 each transmit an RF signal which is sensed by these antennae 301, 303. In this embodiment, at least one Access Point is a wireless router. Each Access Point 210, 220 includes source identification in its signal. This allows the source of a received signal to be determined Therefore, antenna 301 receives the first signal from the closer Access Point 210, and then receives the second signal from farther Access Point 220.

Similarly, antenna 303 receives the signal from the closer Access Point 220, and then receives the signal from farther Access Point 210. This results in four received signals.

The signals received from antennae 301, 303 are provided to an HMD receiver 320 that determines position information. The HMD receiver circuit 320 in this embodiment is built into the HMD 300.

Signals from HMD 300 are provided to an HMD receiver 320. HMD receiver circuit 320 includes a carrier recovery circuit 330 that determines the phase differences between the signals received at the antenna 301 and that received at 303 for both Access Points 210, 220.

HMD receiver 320 also includes a data processor 339 that computes the distances between the RFID tag 601 to each of the HMD antennae 301, 303 by analyzing signal's phase differences.

The phase offset information from the phase comparator 335 is passed to a data processor 339 which knows the distance between the antennae 301, 303 and calculates the relative distance between each of the AP antennae 210, 220 and each of the HMD antennae 301, 303. In this embodiment, the difference in the time of flight (TOF) of the signals is used to determine relative distances. Additional information is required to uniquely identify the position and orientation of the HMD 300.

There is an initial transmission and a return transmission. The initial transmission in this embodiment described above for FIG. 1 has the Access Points 210, 220 initially transmitting to antennae 301, 303, which are each connected to a transceiver on HMD 300. Each transceiver on the HMD 300 creates a signal that is broadcast and sensed by the Access Points 210 and 220. Therefore, Access Point 210 receives a signal broadcast from antenna 301 and from antenna 303. Access Point 220 receives the signal broadcast from antenna 301 and the signal broadcast from antenna 303. The signal from antenna 301 has an embedded ID indicating that it came from antenna 301, while the signal from antenna 303 has an ID embedded in it which identifies that it came from antenna 303. By comparing the transmitted signal received from each transceiver one can determine the phase offset that indicates the difference in distance the signals traveled.

In an alternative embodiment, one can measure the total time it took from sending the initial signal to receiving the response (time-of-flight, “TOF”), taking into account how long it takes the responding transceiver to make a response. The difference in the TOF of the signals from Access Point 210 to antenna 301 and 303 indicates the relative difference in these distances. And similarly, the difference in TOF of the signals from Access Point 220 to antennae 301, 303 indicates their relative distances.

Even though this was described as the Access Points 210, 220 initiating the transmission and then processing the received signal, the situation may be reversed in which the HMD antennae 301, 303 broadcast an initial signal which is received by the Access Points 210, 220. These Access Points 210, 220 then respond by broadcasting a signal which is received by antennae (and their associated transceivers, not shown).

These broadcast signals are then received and processed by electronics in the HMD 300 to determine the distance of each antennae 301, 303 to each of the Access Point antennae 211, 221.

It is understood that all equipment required to process the signal and determine distances may be present in both the HMD 300 and Access Points 210, 220, which also determines the position and orientation of the HMD 300 relative to the Access Points 210, 220.

The position and orientation information of the HMD 300 are then provided to a VR system (or AR system) 250. This may be by a communication link which preferably employs the existing transmitters and receivers. A transmitter—receiver device may be referred to as a “transceiver”. The position information is important in defining the viewpoint used to generate the images provided on display 309. VR system 250 employs at least one processor 251 coupled to memory 253. Memory has pre-stored executable instructions 255. Memory is also used for storage of other information 257.

Throughout this description, reference will be made to mobile devices, including specifically an HMD 300. For purposes of this disclosure and as described below in more detail, the mobile devices are not limited to an HMD 300, but could be virtual or augmented reality glasses, robots, drones, vehicles, handheld communicators, scanners, or any device with radio frequency (RF) communication capability. Similarly, those of ordinary skill in the art will recognize that the Access Points may be any type or number of devices at known locations transmitting a multifrequency RF signal with coordinate information.

HMD Receiver

FIG. 2 shows an HMD receiver 320 capable of independently processing at least two channels of signals, one for the signals received by antenna 301 and the other for signals received by antenna 303 at the HMD 300. In this embodiment, the phase differences of arrival (PDOA) of multifrequency signals sent from Access Point 210, 220 to HMD 300 are used to make range measurements through time of arrival calculations. In this example, the individual antenna receiver channels of HMD receiver 320 independently determine a phase relationship from the multifrequency transmission(s) sent from each Access Point 210, 220. The phase difference measurements are then used to determine time of arrival of the signals sent from the Access Point as they are received by the HMD antenna, and the time of arrival information is then used to determine the distances between antennae 301, 303 and Access Points 210, 220.

In one embodiment for determining phase information, each receive channel of HMD receiver 320 may be comprised of an antenna 301, 303 coupled to an amplifier circuit 321 to amplify the received signal.

The amplifier circuit 321 is coupled to a down-converter 323 to bring the frequency of the signal down to a frequency that can be processed.

Down converter 323 provides the down-converted signal to a filter 325 which passes a signal band that is to be processed.

An analog-to-digital converter (ADC) 327 receives the filtered signal, samples the signal, digitizes the samples and provides them as a stream of digital information.

Each Access Point 210, 220 transmits signals with a specific and known PN code, which is then used by the receiver to de-spread the signal. A digital signal processor 331 is coupled to the ADC 327 and separates out signals on multiple frequency bands using band pass filters (BPF) 337. This may be done by deconvoluting the signal with a particular pseudo-noise (PN) sequence code from a pseudo noise generator (PN) 329.

The system may employ a delay locked loop (DLL) 333 to synchronize with the signal. After the synchronization has occurred, parallel digital filters may be used to separate out multiple frequency components from the signal.

After separating out the frequency components, the phase of each component is extracted and compared using a differential phase comparator 335.

Each frequency band may include a separate set of information. For example, frequency band Freq_1 may include information relating to the signal received by HMD antenna 301 which was transmitted from Access Point 210. Similarly, Freq_2 could have information relating to the signal received by HMD antenna 303 which was transmitted from Access Point 220.

The digital information on the various frequency bands Freq_1, Freq_2 . . . Freq_N can be used to calculate various times of arrival of the signals, various distances and ultimately, the relative position and orientation of the tracked object.

The digital processor then utilizes the phase information to calculate several ranges and then the location and orientation of the HMD from the ranges. One possible technique for calculating range based on multifrequency phase differences from a single transmission source is described in detail in the above-mentioned paper “Multifrequency-Based Range Estimation of RFID Tags” (2009, IEEE, by Xin Li), and is hereby incorporated by reference as if set forth in its entirety herein. According to the Li paper, for a dual frequency continuous wave using frequencies f₁ and f₂, “if the range of an RIND tag is lamer than R_(max)=c/Δf₁₂, which is referred to as the maximum unambiguous range, the phase difference between the two carrier frequencies exceeds 2π. Because phase observations are wrapped within the [0, 2π] range, it yields range ambiguity problem.” The Li paper also states that it is clear from this R_(max) equation that “as far as the maximum unambiguous range R_(max) is concerned, it depends on the difference Δf₁₂ between the two frequencies whereas their absolute values are not relevant . . . . [A] large frequency difference corresponds to a small value of R_(max), e.g., R_(max)=150 m for/MHz, and R_(max)=5 m for Δf₁₂=30 MHz. Thus, to obtain a large maximum unambiguous range value, a small frequency separation is required. Because an RFID system has a finite tag range, adequate frequency separation can be chosen to accommodate unambiguous range estimation. However, . . . decreasing the frequency separation amplifies the sensitivity of the phase difference to noise and thus yields degraded range estimation accuracy. To reduce the sensitivity of the phase difference to noise, therefore, it is necessary to select an adequate value of frequency separation. As a result, the selection of frequency separation should satisfy the requirements for a large maximum unambiguous range and low sensitivity of the phase difference to noise.”

-   -   The relative position of two antennae, with respect to each         other are known. In FIG. 1, antenna 301, 303 are fixed to the         HMD approximately 5 inches apart and on a common plane for ease         of understanding. The extracted phases are utilized to determine         four distances, one being that between each HMD antenna 301, 303         and each Access Point 210, 220. Using this information, the         relative position and orientation of the HMD antenna 301, 303         relative to the Access Points 210, 220 within a 2-dimensional         plane can be determined.

In this first embodiment of FIG. 1, if the wireless Access Point 210 has a known absolute location (X,Y,Z, or any other coordinate system) with respect to a universal coordinate system, the absolute position and location within a 2-dimensional plane may be determined. This physical location is broadcasted as part of, or in addition to, the multiple frequency RF signal sent from the Access Points 210, 220. Similarly, the other Access Points also may transmit their absolute locations.

The use of a system employing a single Access Point may be acceptable in certain applications. For example, if one only requires to measure a distance from the Access Point 210 to an HMD 300, a single Access Point would be adequate. However, it is often desired to precisely determine and track the location and orientation of a mobile device, such as HMD 300. In this case, multiple Access Points would be required.

The present system provides improved location accuracy if there are two Access Points, as shown in FIG. 1, as opposed to a single Access Point. In such a setup, the HMD 300 uses both antennae 301, 303 to determine the distance to the two Access Points 210, 220 as described above based on PDOA information. Each Access Point 210, 220 has a unique PN code that identifies its RF multifrequency signals. Since the antenna 301, 303 have a known spatial separation and the orientation can be determined with motion sensors, the position of the HMD 300 can be determined.

The distance from the Access Points 210, 220 to each HMD antenna 301, 303 is calculated using time of arrival information using PDOA information from the dual or multi frequency signal transmitted by the Access Points 210, 220.

In this case, the two-dimensional (2D) position of the HMD 300 cannot be determined using only two Access Points 210, 220. Since these determine distance from the transmitter in any direction, the possible solutions for a single distance result in a circle around the transmitter. When this process is repeated for a second Access Point, there are now two solution circles that intersect at two locations. This results in two possible solutions. However, once the HMD starts moving, the heading and orientation of the HMD 300 can be utilized to reduce the solution space to a single solution and determine the position of the HMD 300.

In order to calculate the orientation of the HMD 300, in addition to its 2D position, requires an additional Access Point. Trilateration can be performed using the known position information of the two Access Points 210, 220 and position of the HMD antennae 301, 303 as calculated relative to the Access Points 210, 220. For determining 3D position without having motion/orientation sensor information, it is preferred to have four Access Points 210, 220, etc. to perform multi-lateration and accurately determine the position of the HMD 300.

Assuming that the location of each wireless Access Point 210, 220, . . . is transmitted to the HMD, the precise location and orientation of the HMD 300 is now calculable. It will be recognized that further Access Points providing additional multifrequency RF signals incorporating their known positions will further improve system accuracy and resiliency. For system cost reduction, it may be a desirable design choice for multiple transmitters to share a single processor that generates the multifrequency RF signals and unique PN identifier code for each Access Point.

For AR applications, accuracies of less than 5 mm and orientation headings of less than 0.2 degrees are desired. Otherwise, the objects coincide depending on the distance of the object to the viewer. If the object is far away, small orientation errors (<1 degree) will cause the object to move in respect to its background, and for objects that are close to the viewer small errors in position (<1 cm.) will cause the object to move, thus, degrading the AR experience.

To acquire accuracies that are less than a few inches in AR applications, the system improves accuracy using image processing techniques that reduce the computational burden by locking an object's shape and color contrasts. It can also approximate an object's motion in space. For example, the software can perform smoothing of object movement by causing displayed images to move in curves or lines, rather than in a jerky or jittery motion. Various other image-processing techniques can be utilized to improve image presentation.

For example, as seen in FIG. 3, an object, such as a cylinder 5 may sit in front of a mountain 3 (real or virtual). If the cylinder 5 is being tracked and does not move for a period of time, any motion of the object detected when the viewpoint changes, may be rejected or “smoothed” and no object motion would be displayed. The cylinder 5 is thus biased as locked in place relative to other objects in the image unless motion is repeatedly verified over time or verified by multiple Access Points.

At system start-up, a Mobile Device, such as HMD 300 in this example, may be put into a precise known position and orientation relative to the Access Points and the difference between the HMD's calculated position and known position are determined as the calibration error. The system is then adjusted to compensate to use the offset error in calculations to more accurately determine positions.

Motion and orientation sensors may be employed to supplement tracking, as indicated above.

FIG. 4 shows another embodiment of the tracking system according to the present disclosure that utilizes a variety of transmitters 210, 230, 240 to fix either relative position or absolute position of a tracked device, here being HMD 300. The system may adjust to function as several different embodiments.

First Embodiment

In the embodiment shown in FIG. 4, multifrequency RF signals and location information are sent from an Access Point 210 (as described above) and a stationary mobile transmitter 230 (such as a cell phone). The HMD 300 uses the phase difference of arrival relationships from the multifrequency signals received from both the Access Point 210 and the mobile transmitters 230, 240 to determine the locations of HMD antennae 301, 303. In this embodiment, the mobile device transmitter 230 acts much like the second Access Point. More specifically stated, once the Mobile Device 230 location is identified accurately, it transmits multifrequency RF signals and its location to the HMD 300. The distance information from the HMD 300 to the Mobile Devices 230, 240 and Access Point 210 are used to accurately determine the HMD's 300 relative position. Adding the known position of stationary mobile transmitter 230 to the positions relative to mobile device 230 results in absolute positions.

The location of the Mobile Device 230 may be determined in a variety of ways. Preferably, however, the Mobile Device 230 independently determines its position using phase difference of arrival from multifrequency signals from the Access Point 210 (or Multiple Access Points), such as described above. Alternatively, the location of the Mobile Device 230 may be tracked by a networked system by transmitting a signal to a plurality of receivers at fixed locations, such as described in U.S. Pat. No. 8,749,433.

A receiver would then calculate the PDOA either at each Access Point (if Mobile Device sends multifrequency RF signals) to calculate TOA information or by comparing the Mobile Device RF signal's phase at each Access Point to calculate time difference of arrival (TDOA) information. In both approaches, distances are used to perform multi-lateration calculations to determine the position of the Mobile Device and report it back to the Mobile Device.

Determining mobile device position to an accuracy of a few inches or better is needed to enable effective HMD VR or AR functionality. In addition to VR and AR functionality, certain applications for HMDs or other mobile devices require high resolution, highly accurate position tracking functionality. Using phase as a means to extract signal timing information for position detection is an effective means to meet these accuracy requirements.

Networked Tracking

As will be recognized by one of ordinary skill in the art, each transmitter that is being controlled to broadcast a known position using multiple frequency RF signals to another device coupled to a device which has decoding capabilities potentially can calculate distances between the receiving device and the transmitter. Then, each mobile device, such as a radio-frequency identification (RFID) tag that is running software or is otherwise controlled in the proper manner, that has a known position and is stationary (at least for a period of time) can further serve as a reference point, mimicking the function of an Access Point, providing position information to other devices that communicate with it. Therefore, by loading the proper software on such devices, they can create an evolving mesh network of shared position information that will increase geographic coverage and improve location accuracy without requiring additional network hardware such as Access Points.

Automobile Position/Direction Determination

The systems described above may be implemented for various uses. For example, assume the Access Point 210 in FIG. 5 is in the driver's front corner of an automobile (“first car”) 501, and that this automobile is GPS enabled. The automobile 501 has Tags 610, 620 that transmit multifrequency RF signals and location information from antennae 611, 621, consistent with the description above.

A driver in a second car 503 may be wearing an HMD 300 with HMD antennae, or alternatively, may have antennae 301, 303 attached to various parts of the automobile. In this embodiment, they are at the driver's front corner, and the passenger's rear corner of the automobile 503. These multiple antennae 301, 303 are coupled to a processor (not shown) running executable code that perform the tracking functions as described herein. Transceivers connected to antennae 301, 303 receive the multifrequency RF signals transmitted from Tags 610, 620 and transmit signals back to antennae 611, 621. The attached processor in car 501 calculates position and location information based on Time of Arrival information and multi-lateration calculations.

Based on this position information from the second car 503, the system of the first car 501 may determine the speed and projected path of the second car 503. A warning may be issued to the drivers, or in a self-driving or driver-assisted car having a control computer, the computer control, either, or both cars 501, 503 may take evasive measures (braking, turning, etc.) to avoid a collision. It is understood that the situation may be reversed in which the functions described as being performed by automobile 501 may be performed by automobile 503 and vice versa. This embodiment functions in a manner similar to that described in FIG. 6, assuming that FIG. 6 employed two Tags.

It should be recognized that GPS is not the only way to augment the tracking system of the present disclosure. For example, an automobile will commonly include a compass, speedometer, accelerometers and cameras or other sensing devices (radar). These devices may augment the present system of object tracking. For example, a compass and speedometer generally provide bearing and speed. However, driver input may change radically or a car may be moving out of control (i.e., speed and compass are not accurate in a car spinning on ice). In such situations, the present disclosure can augment relative tracking between two or more cars. A second car will have two antennae, and the actual motion of a first car that is transmitting multifrequency signals can be tracked and used to determine if the first car is out of control, getting too close to the first car, etc.

The above descriptions of tracking HMDs is much more broadly applicable when considering that many mobile transmitters and receivers may utilize the present disclosure. For example, the mobile telephone is ubiquitous in the world today, and in the present disclosure, each mobile phone may provide location and tracking services not only to HMDs, but to any other transmitter including other mobile phones, automobiles, scanners, Access Points, etc. Thus, phone-to-phone, car-to-car, phone-to-car are all links that may provide mutual location and tracking services to improve the user experience.

Granularity of Information

In the above embodiments, different aspects of position knowledge are required. Specifically, for an HMD in a virtual reality system, the latency delay in tracking is preferably less than 20 milliseconds. Such can be achieved with a conventional digital signal processor and limited filtering of data.

On the other hand, in the automobile example, location may be determined on a less fine scale and the system may use longer wavelength RF signals that provide greater geographic range, but require larger antennae and result in slower processing speeds. These choices are within the domain of the system designer knowing the utilization parameters (i.e., speed of objects being tracked, tracking accuracy requirement, etc.).

In certain embodiments of the present disclosure, it is important to determine absolute physical location (x,y, or x,y,z position in the physical world). Absolute physical locations are typically identified with respect to a commonly accepted, or a universal reference frame. However, in other embodiments of the disclosure, relative physical location is adequate.

FIG. 6 provides another preferred embodiment that does not require determination of the absolute location of the devices, but can function with relative locations. In this embodiment, a receiving device, such as an HMD 300, determines the position, relative to itself, of other transmitting devices, such as an RFID tag 600 that is capable of transmitting dual or multifrequency radio signal information through its RFID antenna 601.

Signals from HMD 300 are provided to an HMD receiver 320. HMD receiver 320 passes the signals to a carrier recovery circuit 330 that may include a DLL circuit 333 and a phase comparator 335 that determines the phase differences between the received signals. HMD receiver 320 passes the phase differences to a processor 339 that computes the distances between the RFID tag 600 to each of the HMD antennae 301, 303.

This calculation is described above with relation to the HMD calculating its 2-D position relative to the RFID tag 600. In such a system, it would not be possible to determine HMD's 300 absolute position from RFID tag 600 that has unknown positions.

FIG. 7 shows a simple configuration for determining the relative three-dimensional position of an RFID tag 600 relative to the HMD 300. In this embodiment, RFID tag 600 transmits a dual or multifrequency signal and an identification code that is received by at least three HMD antennae 301, 303, 311 placed on or embedded in the HMD 300. These HMD antennae 301, 303, 311 could be placed at the end pieces of the HMD.

In this embodiment, one HMD antenna would compare the phase difference of arrival of the Tags' dual-frequency signal as it is received at each HMD antennae. This received dual-frequency signal phase difference information sent from the RFID tag 600 and received at the individual HMD antennae 301, 303, 311 are then used to determine distances between the RFID tag 600 and each HMD antenna 301, 303, 311. The three distances as determined between each HMD antenna 301, 303, 311 and the RFID tag 600 as well as the antennae's known relative separation from each other and positions on the HMD 300 allows the system, through trilateration or multilateration techniques, to determine the locations of the three HMD antennae 301, 303, 311 relative to the RFID tag 600. These three points define a plane which defines the position and orientation of the HMD 300 in space.

To improve tracking of the relative position of the Tag, motion sensors that may be inside or on the Tag could be utilized to determine the Tag's orientation and acceleration, and then combined with range determined by RF.

The system in FIG. 7 may be utilized with or without knowledge of the exact position of the HMD. In the latter case, the position of the single or multiple RFID tags 600 that are tracked by the HMD 300 may all only be related to the HMD 300. This allows full functionality in a virtual reality environment where HMD 300 and/or RFID tag 600 absolute position detection is not required.

Alternatively, the position of the HMD 300 may be tracked such as is described above with the use of Access Points 210, 220 . . . , and the relative position of the RFID tags 600 may also be derived based on their relative location to the HMD 300. This is more beneficial in an augmented reality system.

Referring back now to FIG. 1, the HMD 300 is fed information from a software program executing in a VR system 250. The software program may be running locally (i.e., at or near the HMD 300) or may be streamed to the HMD 300 from a more distant server/processor, such as VR system 250. The software provides images onto the displays 309 viewed by a user through the HMD 300. In an alternative embodiment, the images may be viewed on the screen of a mobile device.

In the present disclosure, an RFID tag may be attached to the user's hand (or on an object held by the user). Such an RFID tag may be represented in a virtual environment generated by the software as a cursor, ball, weapon or other object. Motion of the hand causes motion of the RFID tag. The HMD 300 tracks motion of the RFID tag 600 and the movement of the Tag is provided to the software providing images to the HMD 300. Thus, the software shows accurate movement of the cursor, ball, weapon, or other object representing the RFID tag 600 on the HMD 300. The RFID tag 600 may also include motion/orientation sensors that provide information to the HMD 300 (along with multifrequency signals and Pseudo Noise information) for further improving position accuracy and intuitive interaction by adding orientation sensing with multiple degrees of freedom beyond the positional tracking.

In addition, or alternatively, position information may be displayed if the relative location of RFID tags on a user is known. For example, if two tags were placed on a user's hand, such as one tag on a thumb and one on a pinkie finger, hand orientation may be displayed in a virtual reality environment based on the position of the two tags relative to each other.

In the particular application of the present disclosure that relates to glasses or an HMD type device, further uses are created by the present disclosure. For example, glasses and HMDs often have earbuds or the like. If the location and orientation of the HMD are determined in an augmented or virtual reality system, the user can be cued by auditory or visual input to turn and look in a particular direction. As a specific example, a user wearing virtual reality glasses driving a car (real or virtual) may be looking forward as determined by the HMD orientation. Detecting this orientation, the augmented or virtual reality program may instruct the user through the earbud (or by visual cue) to “look left at an object” and then provide the appropriate vision for the user as the HMD is tracked to move left. Similarly, the system can track virtual reality objects and provide sensory feedback to the user based on their location. For example, if the user fails to move as determined by the HMD tracker, a buzzer on a part of their body could provide feedback that a virtual ball has “hit” the user.

The above embodiment is broadly described relative to augmented or virtual reality systems, and it might be thought limited to very constrained environments. However, the above system can be integrated with other technology. For example, it is recognized that GPS location does not provide the required accuracy in many environments, and especially indoor environments. However, each GPS may transmit and receive RF signals on multiple frequencies and position information to further expand the mesh network of location tracking devices described above. Alternatively, an RFID tag 600 may be connected to a GPS unit (an HMD or drone, for example). In this situation, the location and orientation of the HMD may be added to the location of each GPS unit to provide more accurate location information.

While the absolute position accuracy of the HMD as determined by the GPS unit is less precise than AR or other HMD applications with high accuracy requirements, in certain use cases, such as the case of tracking multiple automobiles described above, this precision may prove adequate. Triangulation of increasing number of GPS-enabled HMDs or similar Mobile Devices could improve absolute location accuracy. In this situation, for example, one precise position location may be derived from an Access Point, and may be communicated to other Mobile Devices. This will greatly improve the entire system's Mobile Device position detection.

More specifically, turning back to FIG. 4, three devices are illustrated: an Access Point 210, two Mobile Devices 230, 240, and an HMD 300. However, as mentioned above with respect to cars, at different times each device may act as a device being tracked or as a tracking device, provided a device has multiple antennae (or an extension providing multiple antennae) when it is being tracked, the ability to emit multifrequency RF signals, and is running the appropriate software when tracking another device.

For example, in FIG. 4 assume that the Access Point 210 is a Mobile phone that has location information (from GPS, user input, a local area network or other source). The Mobile Phone transmits multifrequency RF signals to a second Mobile Device that has multiple antennae and determines its location as described above. The HMD 300 may be a third Mobile Device, which also receives the multifrequency RF signal from the Mobile phone and likewise determines its location. In this embodiment, the additional information is the relative location of the second and third Mobile Devices as determined using the signal from the Mobile phone.

The above system can be improved for accuracy when each Mobile Device augments the calculated position information with other location/orientation information. Thus, if each Mobile Device includes a GPS, the tracking information may be augmented by sharing GPS locators among the three Mobile Devices. This may allow less frequent transmission of multifrequency signals for location tracking to conserve battery power if the tracking application requires less exact position certitude.

Dealing with ‘Bad Data’

It should be noted that with mobile devices, position and orientation will change with user movement. Further, a mobile device (or even an Access Point) may be broadcasting “bad” position data either through erroneous calculation or for nefarious reasons. There are multiple ways to address such concerns.

In the case of mobile devices, the mobile device will typically contain multiple options for determining gross or accurate position. GPS can provide gross position information, while the above referenced phase determined TOA or TDOA based position calculation systems provide much finer position, and even orientation, detail. Phones often include accelerometers, gyroscopes, and magnetic sensors that may also indicate movement of the mobile device. The central processing unit may be programmed to, for example, cease broadcast of position information if the accelerometer detects movement and the position of that device is unknown due to the movement. Alternatively, one could rely on position movement relative to GPS coordinates to terminate transmission of position information, or a combination of factors may lead to terminating position transmission due to suspected errors. The present disclosure contemplates weighing input from multiple sources to determine if position calculated is accurate. The weight given a position calculation may depend on the perceived credibility of the information source. For example, if a GPS signal indicates a gross position miscalculation and only one Access Point is available, the device may reject the Access Point information. Alternatively, if multiple trusted Access Points are designated as trusted position providers and are consistent in their location calculation, but GPS signal is weak or sporadic (indoors for example) the system may reject GPS information entirely.

On the receiving side when determining position location, it is harder to discriminate bad data. However, incorporating RF multifrequency signals and location information from multiple transmitters can provide redundancy for multiple position data points to determine best fits in predictive models and/or for screening position data not correlated to known system transmitter coordinates. One could also append “trusted source” tags to data position so that a user could elect to only use certain RF transmitters when calculating their absolute position.

The present disclosure may incorporate a variety of possible alternative technologies and be used in a broad range of applications. For example, with respect to an inventory tracking system, there are a plurality of objects being tracked, including but not limited to palettes, crates, robots, scanners, people, cartons, boxes, trucks, etc. Some or all of these objects may include location-tracking capability along with identification ability.

Package Tracking

The RF tracking may utilize, for example, a scanner (Scanner or Reader) to identify and track objects as described in U.S. patent application Ser. No. 14/568,468, filed Dec. 12, 2014, titled “Tracking System with Mobile Reader”, the entirety of which is incorporated by reference herein. Objects can be identified and the location of the object associated with the Scanner's determined position. In such a system, the present disclosure may utilize any identification means like RFID, barcode, etc. The Scanner may, in one embodiment, be an ultra-wideband system that reads ultra-wide transmitters or transceivers placed on boxes and packages. In such an embodiment, three or four ultra-wideband transceivers may be fixed in at least 3 locations within a package storage area, which may be a cargo area, or a package delivery vehicle. Preferably these locations are in the corners, but may be at other suitably spaced locations.

Each package in the truck with a transmitter or transceiver is uniquely identified and located as detailed above by the antennae in the truck. A GPS is typically available in such vehicles and the GPS may be interfaced to the tracking system. Thus, when the driver arrives at a house/business, the GPS identifies the address and specifies the packages that are to be delivered. The tracking system can determine the location in the vehicle of the objects to be delivered to that address and provide the location of the packages to the driver, thus speeding up delivery. Further, if multiple packages are to be delivered, but the tracking system identifies that only one object is removed from the vehicle, the driver can be notified that another package remains in the vehicle to be delivered to the GPS identified address. This type of geo-fence will greatly improve delivery efficiencies.

Since the transceivers transmit over a transmission region larger than the delivery truck, the system may also track the package as it is being carried outside of the delivery truck, but still within the transmission range.

The present disclosure may incorporate a variety of possible alternative technologies and may be used in a broad range of applications. Each of the objects being tracked may include location tracking capability along with identification or information storage ability. Each object may be identified and the location of the object associated with a Scanner identifying the object. Such a system may utilize any identification or information storage means like RFID, barcode, etc., within the scope of the disclosure.

In such a system, the Scanner may determine the position of objects relative to itself (as in the delivery truck example) and can determine its position using one or more antenna mounted on the Scanner and using multifrequency, ultra-wideband, or similar RF signal transmissions to and/or from one or more Access Points with known position coordinates, as described above with relation to the HMD, and/or with other integrated location identifiers (i.e., GPS). The Scanner can read information from RFID, as well as provide location information to the RFID(s). Thus, it will be noted that, similar to the above description of a HMD or GPS, once a Scanner has calculated its position, it may transmit RF signals or other means to deliver data with identifier information and its physical location. Other devices receiving these signals may now calculate their own physical position using the Scanner and other objects' or Access Points' position data.

In an alternative embodiment, an object may need power to provide a signal indicating its location. In which case one could provide power to the device by immersing it in a wireless power field (i.e., Magnetic Resonance, Inductive, time-changing magnetic field, etc.). In such an embodiment, when a device (such as a package) enters a power field, the electronics in the package can ‘power up’ and then communicate with other devices and/or a host system using the same transmitting techniques described in this disclosure.

In one embodiment, a Scanner is utilized to record and store object information and location at which the product was scanned, as shown in above referenced in U.S. patent application Ser. No. 14/568,468. That object will transition through a plurality of facilities such as manufacturing, processing, storage, transportation and retail. Each time the product is scanned, the object information and scan location are read as described in the cited application. However, as shown in FIG. 2, if the package has the proper circuitry to respond to a wireless power field, as the package passes a power field, the electronics on the package (that provide the package's identification and related information) could receive power and transmit the information and/or their location.

In one such embodiment, a package of a perishable material has an RFID chip on it that records temperature. Such are sold by AlienTechnology.com or Zebra.com. When placed in range of a wireless transmitter sending multifrequency signals, the RFID can power up, record the temperature and transmit this information. Note that some systems are battery powered for automated, intermittent temperature recording. In such a system, all recorded temperatures may be transmitted by the RFID on power up. In such a system, any wireless receiver in range of the RFID tag now has two pieces of information: the recorded temperature and a general location of the RFID device. In some systems, this may be adequate, but in a preferred embodiment, the location of the RFID tag would be determined as described above by using multiple receivers to trilaterate or triangulate the tag position. One of ordinary skill in the art will recognize that although RFID and barcode technology are commonly used today to store item identification and/or information, other technologies or protocols for data storage and transmission may be used in the present disclosure.

One of ordinary skill in the art will recognize that the relative fixed locations of the antennae in a device are within the discretion of the system designer. For example, in the HMD example provided above the antennae were stated to be placed 5 inches apart on a plane. In the truck example, the antennae were placed in corners of the vehicle cargo bay. However, the distance and location can be chosen by the designer to optimize the ability of the objects to be located and/or to further track other transmitting devices (Tags, RFID, etc.).

One of ordinary skill in the art will recognize that a variety of wireless transmitters and receivers may be used in the present disclosure. For example, the position of the HMD may be determined relative to transmitted RF signals using varying combinations of tags, mobile devices or fixed devices (routers, hubs, Access Points, etc.) using a variety of communication protocols (BLUETOOTH®, S02.XX, WLAN, ultra-wideband (UWB) and others).

In one embodiment, connecting two or more of the receiver antennae to a single receiver channel provides a major cost savings in hardware and limits circuit board space required by an HMD. In this example, one receiver channel would be used for both receiver antennae on the HMD. To enable this function, we employ a multiplexing technique that will allow the receiver channel to multiplex between each HMD antenna after extracting the PDOA data from the signals sent from the Access Points communicating with each antenna. To accomplish this multiplexing feature, our single (for both antennae) receiver channel would also include a multiplexing switch (MUX), connected to each of the HMD antennae through an electrical connection that will toggle between each antenna.

In an alternative embodiment, there are several nodes set up in spaced locations throughout a building, such as their office or home in which the nodes know their locations. There are several devices which are portable that have the logic of the current invention built into them. These may be tablets, laptops, smartphones and other mobile computing devices which are capable of WI-FI® wireless standards, cellular, and BLUETOOTH® wireless standards, RFID and near-field communications. The current invention may use any of these communication modes as long as the receivers are also capable of receiving these communication modes.

Therefore, the system may have nodes set up to periodically listen for communications from different transmitting devices in an area, such as the building. The nodes then interact with that portable device and with other local nodes to determine the location of the portable device. They also acquire the ID of the portable device and transmit the information along with a time stamp, node to node to an uplink node, through a network to a server where the information is stored in a table. If the portable device is picked up and moved, the system performs the same functions and updates its locations and time stamp in the table. This therefore keeps the last known location of portable devices along with the timestamp.

A user will set up multiple devices this way, such as the laptop, cellphone, tablet, etc. Also, for objects which do not have a built-in transmitter/receiver, a tag can be attached to it, or built into it. For example, the user's keys may have a tag and a unique ID; his wallet can have a tag and unique ID, etc. The user can then look to the table on the server and find the last known location of all of his objects.

In an alternative embodiment, there are several portable objects lying around at various locations in the building within the range of a number of nodes. Think of these as your cellphone, wallet, laptop, keys, etc. These portable objects either have the capability to transmit and receive in several of the communication modes described above, or have a tag attached to them that has these capabilities. If the portable object is within an area to contact at least 4 other transmitters, one of which knows its location, the portable device can determine its location.

A user has a wearable device, or a tag with similar capabilities attached to him/her. As the user moves around the building, the attached tag listens for transmissions from the portable devices, communicates with them to acquire their ID and location. If the portable device is not within an area to determine its location, it may use the tag on the user to determine its location. The information may then be passed back to an Uplink Node, network and server to be stored.

In an alternative embodiment, the user's tag may be the device which stores the location, timestamp and ID of all portable objects so it always has the last known location of all portable devices.

As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method, and computer program product. Thus, aspects of the present invention may be embodied entirely in hardware, entirely in software (including, but not limited to, firmware, program code, resident software, microcode), or in a combination of hardware and software. All such embodiments may generally be referred to herein as a circuit, a module, or a system. In addition, aspects of the present invention may be in the form of a computer program product embodied in one or more computer readable media having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. The computer readable medium may be a non-transitory computer readable storage medium, examples of which include, but are not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination thereof.

As used herein, a computer readable storage medium may be any tangible medium that can contain or store a program for use by or in connection with an instruction execution system, apparatus, device, computer, computing system, computer system, or any programmable machine or device that inputs, processes, and outputs instructions, commands, or data. A non-exhaustive list of specific examples of a computer readable storage medium include an electrical connection having one or more wires, a portable computer diskette, a floppy disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), a USB flash drive, an non-volatile RAM (NVRAM or NOVRAM), an erasable programmable read-only memory (EPROM or Flash memory), a flash memory card, an electrically erasable programmable read-only memory (EEPROM), an optical fiber, a portable compact disc read-only memory (CD-ROM), a DVD-ROM, an optical storage device, a magnetic storage device, or any suitable combination thereof.

A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. As used herein, a computer readable storage medium is not a computer readable propagating signal medium or a propagated signal.

Program code may be embodied as computer-readable instructions stored on or in a computer readable storage medium as, for example, source code, object code, interpretive code, executable code, or combinations thereof. Any standard or proprietary, programming or interpretive language can be used to produce the computer-executable instructions. Examples of such languages include C, C++, Pascal, JAVA, BASIC, Smalltalk, Visual Basic, and Visual C++.

Transmission of program code embodied on a computer readable medium can occur using any appropriate medium including, but not limited to, wireless, wired, optical fiber cable, radio frequency (RF), or any suitable combination thereof.

The program code may execute entirely on a user's device, partly on the user's device, as a stand-alone software package, partly on the user's device and partly on a remote computer or entirely on a remote computer or server. Any such remote computer may be connected to the user's device through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

Additionally, the methods of this invention can be implemented on a special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit element(s), an ASIC or other integrated circuit, a digital signal processor, a hard-wired electronic or logic circuit such as discrete element circuit, a programmable logic device such as PLD, PLA, FPGA, PAL, or the like. In general, any device capable of implementing a state machine that is in turn capable of implementing the proposed methods herein can be used to implement the principles of this invention.

Furthermore, the disclosed methods may be readily implemented in software using object or object-oriented software development environments that provide portable source code that can be used on a variety of computer or workstation platforms. Alternatively, the disclosed system may be implemented partially or fully in hardware using standard logic circuits or a VLSI design. Whether software or hardware is used to implement the systems in accordance with this invention is dependent on the speed and/or efficiency requirements of the system, the particular function, and the particular software or hardware systems or microprocessor or microcomputer systems being utilized. The methods illustrated herein however can be readily implemented in hardware and/or software using any known or later developed systems or structures, devices and/or software by those of ordinary skill in the applicable art from the functional description provided herein and with a general basic knowledge of the computer and image processing arts.

Moreover, the disclosed methods may be readily implemented in software executed on programmed general-purpose computer, a special purpose computer, a microprocessor, or the like. In these instances, the systems and methods of this invention may be implemented as program embedded on personal computer such as JAVA® or CGI script, as a resource residing on a server or graphics workstation, as a plug-in, or the like. The system may also be implemented by physically incorporating the system and method into a software and/or hardware system.

While the aforementioned principles have been described in conjunction with a number of embodiments, it is evident that many alternatives, modifications and variations would be or are apparent to those of ordinary skill in the applicable arts. Accordingly, it is intended to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of this invention. 

What is claimed is:
 1. A system for tracking mobile devices in real time comprising: first and second multifrequency radio frequency (RF) transmitters disposed at known positions, each multifrequency RF transmitter transmitting a multifrequency RF signal conveying identification and the known position of that multifrequency RF transmitter; and a mobile device with a known heading and orientation and disposed within a maximum unambiguous range of the multifrequency RF transmitters, the mobile device comprising: a user display that provides images to a user as viewed from a viewpoint; at least two mobile display antennae, each antenna mounted on the display at a known spatial separation from each other antenna, the at least two mobile display antennae being adapted to receive the multifrequency RF signals transmitted by the first and second multifrequency RF transmitters; a receiver circuit having a carrier recovery circuit that functions to synchronize the multifrequency RF signals received by each of the at least two mobile display antennae, compare phases of multiple frequencies of each multifrequency RF signal received by each of the at least two mobile display antennae and determine phase differences between the compared phases; and a processor, coupled to the receiver circuit, programmed to: receive the phase differences from the receiver circuit; calculate a distance from each multifrequency RF transmitter to each of the at least two mobile display antennae based on the phase differences; calculate a position of each of the at least two mobile display antennae based on the calculated distances, the known positions of the multifrequency RF transmitters, the known spatial separation between the at least two mobile display antennae and the known heading and orientation of the mobile device; and cause a change in the viewpoint of the images provided to the user on the user display of the mobile device using the calculated positions of each of the at least two mobile display antennae.
 2. The system of claim 1, wherein the carrier recovery circuit comprises: a delay locked loop; and a phase comparator for determining a phase difference of the multifrequency RF signals received by each antenna.
 3. The system of claim 1, wherein the receiver circuit comprises: an amplifier circuit to amplify each multifrequency RF signal; a down-converter to reduce a frequency of each amplified signal; a filter to filter each down-converted signal; and an analog-to-digital converter (ADC), that samples each filtered signal into digital data and sends the digital data to a processor.
 4. The system of claim 1, wherein the processor runs executable code to de-spread each multifrequency RF signal using a particular pseudo-noise (PN) sequence code.
 5. The system of claim 1, wherein the processor utilizes parallel digital filters to separate multifrequency components of each received multifrequency RF signal into a plurality of separated signals to determine a phase of at least two separated signals and compare the phases using a differential phase comparator.
 6. The system of claim 1, further comprising: a third multifrequency RF transmitter, wherein the processor of the mobile device calculates a position of the third multifrequency RF transmitter relative to the at least two mobile display antennae based on phase difference of arrival of a multifrequency RF signal transmitted by the third multifrequency RF transmitter and received at the at least two mobile display antennae, and the known spatial separation of the at least two mobile display antennae on the display.
 7. The system of claim 6 wherein the third multifrequency RF transmitter is an RFID transmitter that receives and retransmits multifrequency signals transmitted from the mobile device.
 8. The system of claim 7, wherein the transmitters and the receiver circuit utilize ultra-wideband communication to determine time of arrival for distances between each transmitter and the at least two mobile display antennae.
 9. The system of claim 6, wherein the calculated position of the third RF transmitter is registered with images shown in the user display.
 10. The system of claim 6, wherein the third RF transmitter is a peripheral device that interacts with the mobile device.
 11. The system of claim 1, wherein the mobile device is a head mounted display (HMD.
 12. The system of claim 1, further comprising two access points, each access point comprising one of the multifrequency RF transmitters.
 13. The system of claim 12, wherein one of the two access points is a wireless router.
 14. The system of claim 1, wherein the mobile device further comprises one or more sensors adapted to provide the known heading and orientation of the mobile device.
 15. The system of claim 1, wherein the spatial separation between the at least two mobile display antennae is five inches.
 16. The system of claim 1, wherein the receiver circuit has an independent receiver channel for each of the at least two mobile display antennae.
 17. The system of claim 1, wherein the receiver circuit has a receiver channel shared by the at least two mobile display antennae.
 18. A method for tracking a mobile device in real time comprising the steps of: determining heading and orientation of the mobile device; transmitting, by first and second radio frequency (RF) transmitters disposed at known positions that are within a maximum unambiguous range of the mobile device, multifrequency RF signals; conveying the known position and identification of each RF transmitter in the multifrequency RF signal transmitted by that RF transmitter; receiving the multifrequency RF signals by two antennae operably coupled to the mobile device with a known spatial separation on the mobile device; comparing phases of multiple frequencies of each multifrequency RF signal received by each of the two antennae; determining phase differences between the compared phases; calculating a distance from each RF transmitter to each of the two antennae based on the phase differences; calculating a position of each of the two antennae based on the calculated distances, the known positions of the RF transmitters, the known spatial separation of the antennae on the display, and the orientation and heading of the mobile device; and displaying images on a display of the mobile device from a viewpoint based upon the calculated positions of the two antennae. 